The present invention relates generally to differentials, and more particularly to a differential equipped with worm gearsets.
Differentials equipped with worm gearsets, such as that shown in U.S. Pat. No. 5,338,267, are known in the art. As is seen, the worm gearsets include a meshed worm and worm gear. One or more such worm gearsets are used in worm differentials to provide power transfer and speed differentiation features. However, the torque capacity of such worm differentials has limited their applications due to the low torque capacity associated with conventional worm gearsets.
As is common throughout the automotive industry, efforts are being made to reduce the size and weight of automobile components. The reduced weight helps improve fuel economy while the reduced size increases packaging efficiency. With regard to worm differentials, the size of the worm and worm gears as well as the number of worm gearsets that are required impact the overall size and weight of the differential. However, a reduction in size and weight of the gear components of a worm differential results in an undesirable decrease in the torque capacity of the differential unit.
Accordingly, it is desirable in the art of worm differentials to provide a differential unit which can be made with reduced size and weight but which does not have an associated undesirable decrease in torque capacity.
It is an object of the present invention to provide a worm-type differential unit which has a higher torque capacity than comparably sized standard worm differentials.
It is another object of the present invention to provide a worm differential unit which can be made smaller and lighter in weight than conventional worm differentials without the reduction in torque capacity associated with reducing the size and weight of the gear components.
Accordingly, the present invention provides a worm differential unit including a differential case adapted to be driven rotationally via a drive gear fixed thereto. A pair of worm gears are supported by the differential case with each worm gear adapted for connection to a corresponding axle shaft. The worm gears are arranged coaxially and are independently rotatable. Paired sets of compound gears are also supported by the differential case. Each of the compound gears has a first segment which matingly engages with one of the enveloping worm gears and a second segment which matingly engages with a corresponding second segment of the other compound gear of the pair. The first segment of each compound gear is an enveloping-type worm. The use of a double enveloping worm/worm gear transmission allows for surface contact between the thread of the worm and the teeth of the worm gear so that a greater torque capacity can be obtained in comparison to the line contact which is obtained with the standard worm gearsets. In addition, the use of double enveloping worm and worm gears allows the gear elements to be mounted on an axis which is closer to the axis of the axle shafts. Furthermore, because of the higher torque capacity of the double enveloping worm and worm gear, fewer pairs of gearsets can be utilized than is typically desired in a standard worm differentials. For example, the standard worm differential typically uses three element gear pairs disposed at 120 degree intervals around the worm gears in order to provide the desired torque capacity. However, due to the increased torque capacity of the double enveloping worm and worm gear according to the present invention, two pairs of gear elements may be utilized without a corresponding reduction in torque capacity but providing a substantial weight reduction.
The present invention also discloses that the enveloping worms utilized with the worm differential according to the present invention can be split worms, thereby further contributing to a reduction in the weight and size requirements of the differential. Furthermore, the present invention also enables heavy duty worm differentials to be made with little or no weight increase in comparison with conventional worm differentials.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.